Cre/Flp Activity in Pig Cells. Individual puromycin resistant PEGE colonies were isolated and expanded for analysis. A) A diagram of the pT2-FloxP-PTK vector showing the location of restriction enzyme sites for SspI and the location of the PTK probe (diagonal lined rectangle). B) Southern analysis shows the number and size of vector inserts in several PEGE clones. The expected concatemer size of 5.6 kb (vertical lined arrow) as well as the smallest possible transposition event (open arrow) of 3.3 kb are indicated on the left of the image. An asterisk is placed to the right of a band slightly smaller than 2 kb in lane 2 (Clone #6). C) The rate of gancyclovir resistant colony formation after transfection of PEGE clones with pPGK-nlsCre (CRE), pKT2-nlsFlp (FLP), or pKT2C-EGFP (GFP). Values that are significantly different from the background (GFP) as determined by an unpaired t-test (p = 0.05) are designated with an asterik (*).